The discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
The present invention is a development of our earlier invention described in WO 2004/028910 (our PCT specification), the equivalent New Zealand patent specification No. 521694, both of which are herein incorporated in their entirety where appropriate by way of reference. However, for the sake of completeness substantial portions of our PCT specification will be included in this present specification.
So called ‘hot fill’ containers are well known in prior art, whereby manufacturers supply PET containers for various liquids which are filled into the containers and the liquid product is at an elevated temperature, typically at or around 85 degrees C. (185 degrees F.).
The container is manufactured to withstand the thermal shock of holding a heated liquid, resulting in a ‘heat-set’ plastic container. This thermal shock is a result of either introducing the liquid hot at filling, or heating the liquid after it is introduced into the container.
Once the liquid cools down in a capped container, however, the volume of the liquid in the container reduces, creating a vacuum within the container. This liquid shrinkage results in vacuum pressures that pull inwardly on the side and end walls of the container. This in turn leads to deformation in the walls of plastic bottles if they are not constructed rigidly enough to resist such force.
Typically, vacuum pressures have been accommodated by the use of vacuum panels, which distort inwardly under vacuum pressure. Prior art reveals many vertically oriented vacuum panels that allow containers to withstand the rigors of a hot fill procedure. Such vertically oriented vacuum panels generally lie parallel to the longitudinal axis of a container and flex inwardly under vacuum pressure toward this longitudinal axis.
In addition to the vertically oriented vacuum panels, many prior art containers also have flexible base regions to provide additional vacuum compensation. Many prior art containers designed for hot-filling have various modifications to their end-walls, or base regions to allow for as much inward flexure as possible to accommodate at least some of the vacuum pressure generated within the container.
All such prior art, however, provides for flat or inwardly inclined, or recessed base surfaces. These have been modified to be susceptible to as much further inward deflection as possible. As the base region yields to the force, it is drawn into a more inclined position than prior to having vacuum force applied.
Unfortunately, however, the force generated under vacuum to pull longitudinally on the base region is only half that force generated in the transverse direction at the same time. Therefore, vertically oriented vacuum panels are able to react to force more easily than a panel placed in the base. Further, there is a lot more surface area available around the circumference of a container than in the end-wall. Therefore, adequate vacuum compensation can only be achieved by placing vertically-oriented vacuum panels over a substantial portion of the circumferential wall area of a container, typically 60% of the available area.
Even with such substantial displacement of vertically-oriented panels, however, the container requires further strengthening to prevent distortion under the vacuum force.
The liquid shrinkage derived from liquid cooling, causes a build up of vacuum pressure. Vacuum panels deflect toward this negative pressure, to a degree lessening the vacuum force, by effectively creating a smaller container to better accommodate the smaller volume of contents. However, this smaller shape is held in place by the generating vacuum force. The more difficult the structure is to deflect inwardly, the more vacuum force will be generated. In prior art, a substantial amount of vacuum is still present in the container and this tends to distort the overall shape unless a large, annular strengthening ring is provided in horizontal, or transverse, orientation at least a ⅓ of the distance from an end to the container.
Considering this, it has become accepted knowledge to believe that it is impossible to provide for full vacuum compensation through modification to the end-wall or base region alone. The base region offers very little surface area, compared to the side walls, and reacts to force at half the rate of the side walls.
Therefore it has become accepted practice to only expect partial assistance to the overall vacuum compensation to be generated through the base area. Further, even if the base region could provide for enough flexure to accommodate all liquid shrinkage within the container, there would be a significant vacuum force present, and significant stress on the base standing ring. This would place force on the sidewalls also, and to prevent distortion the smooth sidewalls would have to be much thicker in material distribution, be strengthened by ribbing or the like, or be placed into shapes more compatible to mechanical distortion (for example be square instead of circular).
For this reason it has not been possible to provide container designs in plastic that do not have typical prior art vacuum panels that are vertically oriented on the sidewall. Many manufacturers have therefore been unable to commercialize plastic designs that are the same as their glass bottle designs with smooth sidewalls.
U.S. Pat. No. 6,595,380 (Silvers), claims to provide for full vacuum compensation through the base region without requiring positioning of vertically oriented vacuum panels on the smooth sidewalls. This is suggested by combining techniques well-known and practiced in the prior art. Silvers provides for a slightly inwardly domed, and recessed base region to provide further inward movement under vacuum pressure. However, the technique disclosed, and the stated percentage areas required for efficiency are not considered by the present applicant to provide a viable solution to the problem.
In fact, flexure in the base region is recognised to be greatest in a horizontally flat base region, and maximizing such flat portions on the base has been well practiced and found to be unable to provide enough vacuum compensation to avoid also employing vertically oriented vacuum panels.
Silvers does provide for the base region to be strengthened by coupling it to the standing ring of the container, in order to assist preventing unwanted outward movement of the inwardly inclined or flat portion when a heated liquid builds up initial internal pressure in a newly filled and capped container. This coupling is achieved by rib structures, which also serve to strengthen the flat region. Whilst this may strengthen the region in order to allow more vacuum force to be applied to it, the ribs conversely further reduce flexibility within the base region, and therefore reduce flexibility.
It is believed by the present applicant that the specific ‘ribbed’ method proposed by Silvers could only provide for approximately 35% of the vacuum compensation that is required, as the modified end-wall is not considered capable of sufficient inward flexure to fully account for the liquid shrinkage that would occur. Therefore a strong maintenance of vacuum pressure is expected to occur. Containers employing such base structure therefore still require significant thickening of the sidewalls, and as this is done the base region also becomes thicker during manufacturing. The result is a less flexible base region, which in turn also reduces the efficiency of the vacuum compensation achieved.
The present invention relates to a hot-fill container which is also a development of the hot-fill container described in our international application WO 02/18213 (the earlier PCT specification), which specification is also incorporated herein in its entirety where appropriate.
The earlier PCT specification backgrounds the design of hot-fill containers and the problems with such designs which were overcome or at least ameliorated by the design disclosed in the earlier PCT specification.
In the earlier PCT specification a semi-rigid container was provided that had a substantially vertically folding vacuum panel portion. Such a transversely oriented vacuum panel portion included an initiator portion and a control portion which generally resisted being expanded from the collapsed state.
Further described in the earlier PCT specification is the inclusion of the vacuum panels at various positions along the container wall.
A problem exists when locating such a panel in the end-wall or base region, whereby stability may be compromised if the panel does not move far enough into the container longitudinally to no longer form part of the container touching the surface the container stands on.
A further problem exists when utilizing a transverse panel in the base end-wall due to the potential for shock deflection of the inverted panel when a full and capped container is dropped. This may occur on a container with soft and unstructured walls that is dropped directly on its side. The shock deflection of the sidewalls causes a shock-wave of internal pressure that acts on the panel. In such cases improved panel configurations are desired that further prevent panel roll-out, or initiator region configurations utilized that optimize for resistance to such reversion displacement.
With the current proposal to incorporate vacuum panels into the bottom end wall of the container so that the sidewalls may remain substantially smooth, the vacuum panels in the bottom wall create a handling problem. When these vacuum panels are extended longitudinally to the outwardly inclined position, the container no longer has a flat bottom surface and the container is, therefore, geometrically unstable.
To overcome any instability of the container during the process of filling with liquid, cooling and labelling, it is well practised in prior art to attach a ‘base cup’ of sorts to the lower end of an unstable container. Attached base cups allow a geometrically unstable container to be supported correctly while the container is transferred through the bottle filling system.
The term “base cup” used hereinafter in respect of the present invention means any holder or holding or transporting means whether in the form of a “cup” or in any other suitable form.
Alberghini, U.S. Pat. No. 4,241,839; Jakobsen, U.S. Pat. No. 4,293,359; Chang U.S. Pat. No. 4,438,856; Nickel U.S. Pat. No. 4,326,638 and many others provide stabilising base cups for containers that are vertically unstable when placed in an upright position. However, in order to process the container of the present invention, whereby force needs to be applied to the bottom end wall, it is necessary to provide an opening through the bottom wall of such a base cup.
Accordingly, there is a need for a system and method of handling containers according to the present invention when the vacuum panel is placed into the geometrically unstable position of being downwardly inclined, whereby stability is imparted to the container, but the vacuum panel is able to be manipulated from one inclination to another.